1. Field of the Invention
The present invention relates to a color imaging device and a color imaging device manufacturing method.
2. Description of the Related Art
In a conventional color imaging device, color filters of a plurality of colors are formed to be adjacent to each other without gaps therebetween by using a photolithography technology on a plurality of photoelectric transducers provided on a semiconductor substrate. Each color filter has a thickness of approximately 1 μm. It should be noted that the color filters include a colorless filter.
In recent years, high pixelation of the imaging device advances, and the number of pixels of the imaging device has recently reached the millions. Further, with such advancement of high pixelation, a percentage of an area occupied by various wiring lines and electronic circuits required to operate each pixel is increased in each pixel. As a result, a percentage of an area that can be actually utilized for the photoelectric transducers to receive light (a numerical aperture) is currently approximately 20 to 40% in each pixel. This means that the luminous sensitivity of the imaging device is reduced.
JP-A 1984-122193 (KOKAI), JP-A 1985-38989 (KOKAI), JP-A 1985-53073 (KOKAI), and JP-A 2005-294467 (KOKAI) disclose that a microlens is arranged on each color filter to associate with each photoelectric transducer in order to improve the luminous sensitivity of an imaging device.
JP-A 1984-198754 (KOKAI) discloses that a hemispherical colored microlens is used as a color filter.
JP-A 2005-217439 (KOKAI) and JP-A 2005-223084 (KOKAI) disclose that arranging a photoelectric transducer at a position as close to a surface of a semiconductor substrate as possible in the semiconductor substrate configuring an imaging device enables increasing a light quantity that can be received by the photoelectric transducer, thereby improving the sensitivity of the imaging device.
FIG. 8 schematically shows a conventional example where microlenses are arranged on color filters to associate with photoelectric transducers in order to improve the luminous sensitivity of an imaging device. In this conventional example, in order to improve the luminous sensitivity of an imaging device 54 having a plurality of photoelectric transducers 52 provided in a semiconductor substrate 50, microlenses 64 are arranged on the surfaces of color filters 58 and 60 of a plurality of colors via a transparent flattening layer 62, the color filters 58 and 60 being provided on a surface of the semiconductor substrate 50 via an ultraviolet absorbing layer 56 to associate with the plurality of photoelectric transducers 52.
However, in this conventional example, color mixing tends to occur in light near side surfaces of the color filters 58 and 60 of the plurality of colors that are adjacently in contact with each other without gaps therebetween. That is, a part of a light beam 66 that has obliquely entered a part of the side surface of the color filter 58 close to the microlens 64 is transmitted through a corner portion including the part of the side surface of the color filter 58 and enters the adjacent color filter 60, thus resulting in color mixing in light near the side surface of the adjacent color filter 60.
In the photoelectric transducer 52 where color mixing has occurred (the photoelectric transducer associated with the color filter denoted by reference number 60 in FIG. 8), color reproducibility and luminosity are reduced, and color shading occurs in the entire imaging device 54.
Furthermore, such entering of a part of light from the adjacent color filter tends to occur when an incidence angle of light entering the photoelectric transducer becomes shallower.
FIG. 9 schematically shows a conventional imaging device 74 in which a plurality of photoelectric transducers 72 are provided to be adjacent to a surface of a semiconductor substrate 70 in the semiconductor substrate 70 in order to improve the luminous sensitivity. Here, color filters 76 and 78 of a plurality of colors are arranged on the surface of the semiconductor substrate 70 to associate with the plurality of photoelectric transducers 72.
In this case using no microlens, a part of a light beam 80 that has obliquely entered a part of one of side surfaces of the plurality of color filters 76 and 78 (e.g., a part of a side surface of the color filter 76 in FIG. 9), the side surfaces being adjacently in contact without gaps therebetween and the part of one of the side surfaces being close to a surface of the color filter, may enter an adjacent color filter (the color filter 78 in FIG. 9) from a side surface of the adjacent color filter like the above described case using the microlenses. In this case, color mixing occurs in the light near the side surface of the adjacent color filter, thus obtaining the same result as described above.
In this case, like the above described case, entering of a part of the light from the adjacent color filter tends to occur when an incidence angle of the light entering the photoelectric transducer becomes shallow.
In order to avoid such color mixing, JP-A 2005-294467 (KOKAI) discloses a technology by which an upper portion of a color filter and a transparent resin mounted on an upper surface of the color filter configure a microlens. That is, the transparent resin mounted on the upper surface of the color filter configures an upper portion of a curved surface of a convex microlens, and then an upper region of the color filter formed to be continuous with a curvature of the upper portion of the curved surface of the convex microlens configured by the transparent resin configures a lower portion of the microlens.
Further, such a microlens is formed by transferring a shape of a lens mother model formed on the surface of the transparent resin onto the transparent resin and the upper region of the color filter through dry etching using the lens mother model as a mask. However, when different color filters are dry-etched under the same etching conditions, the etching rate varies depending on the different color filters. As a result, when each of the upper regions of the different color filters that are adjacent to each other is formed by dry etching to have a curvature that is continuous with the curved surface of the convex microlens formed of the transparent resin, the curvature varies depending on each of the upper regions of the different color filters. Furthermore, a degree of surface roughness also varies depending on each of the upper regions of the different color filters formed to be continuous with the curved convex surface of the microlens by dry etching. Moreover, a balance of colors of light entering the plurality of photoelectric transducers associated with the color filters of the plurality of colors through the color filters of the plurality of colors is degraded, thereby producing color shading in the entire color imaging device.
In the conventional case using the hemispherical colored microlens as a color filter to improve the luminous sensitivity of the imaging device, there is a difference in a length of a light path of light transmitted through the microlens after entering the microlens between a central portion of the microlens and a peripheral portion thereof. When there is the difference in the length of the light path transmitted through the color filter, coloring of a light beam transmitted through each light path differs from each other. As a result, a great difference in spectral characteristics occurs in light beams transmitted through the central portion of the microlens and the peripheral portion thereof.
Since a light quantity transmitted through the central portion is larger than a light quantity transmitted through the peripheral portion in the microlens, light transmitted through the microlens colored to also serve as a color filter has a pale color as a whole. This means that the microlens colored to also serve as the color filter has a low color separation capability.
On the other hand, when coloring in the microlens colored to also serve as the color filter is heightened, the luminosity of light transmitted through such a microlens is lowered. Additionally, when an amount of a coloring agent contained in the microlens is increased, smoothness of the surface of the microlens is degraded, and a function as the microlens is lowered.